/*
day454 
2020.11.24 
*/
#include<iostream>
#include<vector>
using namespace std;

class Solution {
public:
    int missingNumber(vector<int>& nums) {
		int res=0;
		for(int i=0;i<nums.size();++i)
		{
			res^=i;
			res^=nums[i];
		}
		
		res^=nums.size();
		return res;
    }
};


int main()
{
	return 0;
}
